Design

Setting

11 general practices in Edinburgh, Scotland, UK.

Participants

1592 men and women aged 55 to 74 years randomly selected from age-sex registers.

Assessment of risk factors

At the baseline assessment, a questionnaire was used to collect data on smoking history,
history of diabetes, and angina. A clinical examination included blood pressure assessment,
measurement of ankle systolic pressures, 12-lead electrocardiography, and a laboratory
assessment of lipid levels and response to a glucose load.

Main outcome measures

Incidence of fatal and nonfatal cardiovascular events and all-cause mortality.

Main results

At baseline, 90 participants (6%) had an ankle brachial pressure index ≤ 0.7, 288
(18%) had an index ≤ 0.9, and 566 (36%) had an index ≤ 1.0. During the 5-year follow-up
period, 144 participants (9%) had a myocardial infarction (MI); 55 of these particpants
died. A stroke occurred in 50 participants (3%), and 22 strokes were fatal. Of the
203 deaths, 89 (44%) were caused by cardiovascular factors. After adjustment for age,
sex, coronary disease, and diabetes, participants with a baseline ankle brachial pressure
index ≤ 0.9 had an increased risk for stroke (relative risk [RR] 1.98, 95% CI 1.05
to 3.77), cardiovascular death (RR 1.85, CI 1.15 to 2.97), and all-cause mortality
(RR 1.58, CI 1.14 to 2.18). The likelihood ratios for fatal and nonfatal cardiovascular
events at 5 years were 1.76 for indexes ≤ 0.9 and 3.07 for indexes ≤ 0.7. The ability
to predict subsequent events was enhanced when the ankle brachial pressure index was
combined with other risk factors. For example, the positive predictive value for a
future cardiovascular event in a participant who smoked, had hypertension, and had
a normal cholesterol level was 25%, but this value increased to 44% in participants
who also had a low ankle brachial pressure index (≤ 0.9) and decreased to 16% in those
who had a higher index.

Conclusion

A low ankle brachial pressure index was associated with an increased risk for stroke,
cardiovascular death, and all-cause mortality.

Commentary

In essence, a low ankle brachial pressure index equals peripheral artery disease.
It is not surprising that a low pressure index is associated with a high risk for
other manifestations of cardiovascular disease, such as MI and stroke. The strength
of this study by Leng and colleagues is that it puts these associations into a clinically
meaningful context. The important question is this: In routine clinical practice,
is there added value in using measurement of ankle brachial pressure index together
with conventional predictors of MI and stroke?

Leng and colleagues have shown that in patients with none or only 1 of the risk factors
for a future cardiovascular event, the index provides additional predictive information.
Severe peripheral artery disease with gangrene mainly affects patients who smoke or
have diabetes (and particularly patients with both characteristics). It would have
been useful to know the marginal value of the pressure index when diabetes is added
to the other 3 conventional risk indicators.

The virtue of the ankle brachial pressure index is that it is simple, quick, and inexpensive
and can easily be introduced into routine clinical practice. The problem with the
pressure index, however, is that its sensitivity as a predictor of cardiovascular
events is low (30% in this study). On the basis of the figures Leng and colleagues
provide, eighteen 55- to 74-year-old Scottish men and women would have a pressure
index ≤ 0.9 if 100 were screened. Of the 18, 3 would have a cardiovascular event (MI,
stroke, or any vascular death) in the next 5 years. According to the data provided
by Leng and colleagues, 2 of the 3 patients with an event would already have been
identified by a tobacco history, blood pressure, and serum lipid levels. During the
5 years, nearly 3 times as many cardiovascular events (8 events) would occur among
the 82 persons who had a normal pressure index.

Arithmetic exercises such as these show the problems involved in screening and predictions;
the calculations would give similarly modest results if the added value of other risk
indicators was assessed. The important message is that no single risk indicator for
cardiovascular events is powerful enough on its own. The ankle brachial pressure index
is one of the many fragments that, when put together with other bits of clinical information,
helps to provide a more detailed clinical picture of the patient at risk for MI and
stroke.